Permethrin 1% lotion (sold as Nix) is the most widely recommended first-line treatment for head lice and is available without a prescription. It works by attacking the nervous system of live lice, killing them on contact. But permethrin is just one option, and lice in some regions have developed resistance to it, which means you may need a different product or approach depending on how your infestation responds.
Over-the-Counter Lice Shampoos
Two types of lice-killing shampoos are available at most drugstores without a prescription. They use different active ingredients but work in a similar way: both are neurotoxic to lice, meaning they paralyze and kill the insects on contact.
Permethrin 1% (Nix): This is the standard first choice. It’s a synthetic version of a natural insecticide found in chrysanthemum flowers. You apply it to clean, towel-dried hair, leave it on for 10 minutes, then rinse. Permethrin is approved for children as young as two months old, making it one of the safest options for very young kids. It does not reliably kill eggs (nits), so a second treatment 7 to 9 days later is needed to catch newly hatched lice before they can lay more eggs.
Pyrethrins with piperonyl butoxide (Rid): These are natural extracts from chrysanthemum plants, boosted by an additive that makes them more effective. They work similarly to permethrin but are approved only for children two and older. If you or your child is allergic to chrysanthemums or ragweed, skip this one entirely. Like permethrin, pyrethrins don’t kill all eggs, so you’ll need a repeat application on the same 7-to-9-day schedule.
When Over-the-Counter Products Don’t Work
Lice resistance to permethrin and pyrethrins has been growing for years. If you’ve completed two rounds of treatment and still see live lice crawling, the product isn’t failing because you used it wrong. The lice in your area may simply be resistant. At that point, it’s time to move to a prescription treatment.
Spinosad 0.9% (Natroba): This prescription suspension is derived from a naturally occurring soil bacterium. It kills both live lice and eggs, which means many people need only a single application. If live lice are still present seven days later, a second treatment can be applied.
Ivermectin 0.5% (Sklice): Applied once to dry hair, left on for 10 minutes, and rinsed with water. Like spinosad, it often works in a single treatment. It does not kill eggs, but studies show the drug is effective enough against newly hatched nymphs that retreatment is frequently unnecessary.
Malathion 0.5% (Ovide): A stronger option for children six and older. This lotion is left on the hair to air-dry, which takes 8 to 12 hours. One important safety note: malathion is flammable. Do not use hair dryers, curling irons, flat irons, or any electrical heat source while the product is on the hair, and keep it away from open flames.
Silicone-Based (Non-Pesticide) Treatments
If you’d rather avoid insecticides altogether, dimethicone-based products (sold as Nix Ultra or Lice MD) take a completely different approach. Instead of poisoning lice, they physically coat the insects and suffocate them by blocking the tiny openings they use to breathe. Because this mechanism doesn’t involve a chemical attack on the nervous system, lice can’t develop resistance to it.
Clinical studies show that 70% to 96% of patients treated with 100% dimethicone are lice-free at 14 days. That’s a wide range, and results depend partly on how thoroughly the product is applied. The Canadian Paediatric Society recommends dimethicone as a second-line treatment if permethrin fails after two rounds. Like most non-prescription options, dimethicone does not reliably kill eggs, so a repeat application is typically needed.
Do Essential Oils Kill Lice?
Tea tree oil and eucalyptus oil show genuine lice-killing activity in lab settings. In controlled filter-paper tests, tea tree oil at a 1% concentration killed up to 100% of lice on contact, and eucalyptus oil killed lice in as little as four to five minutes. Many essential oils also appear to have some ability to kill eggs, which is an advantage over permethrin and pyrethrins.
The catch is that lab results don’t always translate to real-world performance on a child’s head. Very few clinical trials have tested essential oil products under the messy, imperfect conditions of actual use. The concentrations, formulations, and application times vary wildly between commercial products, and there’s no standardized essential oil lice shampoo with consistent FDA oversight. If you choose this route, look for products that combine tea tree or eucalyptus oil with a physical suffocating agent, which have shown more reliable results in the limited clinical trials available.
Why the Second Treatment Matters
Most lice treatments, whether over-the-counter or prescription, do not kill every single egg glued to the hair shaft. Lice eggs hatch in about 7 to 9 days. The goal of the second treatment is to catch all newly hatched nymphs after the eggs have opened but before those nymphs are old enough to lay new eggs themselves. Skipping the second treatment is the single most common reason lice come back.
The CDC’s guidance is straightforward: if your product kills lice but not eggs, treat again 7 to 9 days after the first application. The specific day depends on the product, so check the box instructions carefully.
Combing Out Nits
No shampoo replaces a good lice comb. A fine-toothed metal nit comb with teeth spaced no more than 0.3 mm apart physically removes both live lice and the eggs that shampoos miss. Used alongside a chemical or suffocation treatment, combing significantly improves your chances of clearing an infestation completely.
The process is tedious but effective. Section the hair while it’s wet and coated in regular conditioner (which slows lice down and makes them easier to comb out). Pull the comb from the scalp all the way to the tips of the hair, wiping it on a white paper towel after each pass so you can see what you’re removing. Repeat this every three to four days for two full weeks. That schedule catches any nymphs that hatch between sessions before they mature enough to reproduce. Dead nits can stay glued to the hair for months even after successful treatment, so finding a nit doesn’t necessarily mean you still have an active infestation. The question is whether you’re finding live, moving lice.
Cleaning Your Home After Treatment
Lice die within one to two days once they fall off a human head, because they need blood meals to survive. That limits how much household cleaning you actually need to do. Wash pillowcases, sheets, and any hats or scarves worn in the last two days in hot water (at least 130°F) and dry them on high heat. For items that can’t be washed, seal them in a plastic bag for two weeks. Vacuum upholstered furniture and car seats. You do not need to fumigate the house, bag up every stuffed animal, or treat pets. Lice are human parasites and cannot survive on animals.
Spending hours deep-cleaning the entire house is unnecessary and takes time away from what actually matters: thorough treatment and combing on the head itself.